This invention relates to a digital image information data reproducing apparatus and more particularly to a replay equalization circuit suitable for variable speed replay.
The relative speed of the VTR tape/head is expressed as a function of the head rotating speed, the winding angle of the tape on the drum and the tape running speed. The tape/head relative speed increases as the tape running speed is increased as during the fast forward.
U.S. Pat. No. 4,577,241 describes a clock recovery circuit using a PLL (phase locked loop) circuit, which extracts clocks from the recorded data on the tape that match the replay speed when the digital VTR is replayed at a tape/head relative speed different from that for recording as during the fast forward. (This replay is simply referred to as a variable speed replay.) However, since the frequency characteristic required to obtain the replay signals from the tape changes according to the replay speed, some measures to adjust the equalization circuit for changes in the replay speed in order to reproduce a quality picture must be provided, not only in the clock recovery circuit but also in the equalization circuit--which compensates for the tape/head frequency characteristic during the recording and reproducing process. So far, however, no reference has been made to this point. Nor have any corrective steps been taken.
In the conventional apparatus, the equalizing frequency characteristic of the replay equalization circuit is constant during the variable speed replay. Therefore, the replay equalization circuit fails to match the increased tape/head relative speed and thus produces inter-symbol interference. This in turn deteriorates an eye opening factor--which represents the state of equalization--increasing the code error.
The same problem that occurs when the tape is fast-fed during replay at a speed higher than that during recording with the digital VTR's also exists with other types of digital image information reproducing apparatuses, which consist of a recording medium corresponding to the tape, a recording/reproducing transducer corresponding to the head, and a replay equalization circuit.